sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 6.5-7 (Mohs), Color: Grey, black, or brown, Luster: Waxy to dull, Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65

Hardness: 6

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: Grey, black, or brown, Luster: Waxy to dull, Structure: Microcrystalline/Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments where silica replaces calcite in limestone. Dates from Precambrian to Holocene.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Currently used as road aggregate, in glass manufacturing, and as flint for fire-starting.

Geological facts

Flint is a variety of chert. It was the primary material for the Stone Age technology because of its predictable conchoidal fracture which allows for the creation of razor-sharp edges.

Field identification & locations

Identify in the field by its waxy luster, extreme hardness (scratches glass), and shell-like (conchoidal) fracture pattern. Often found as nodules in limestone or chalk beds.